Anti-transient showerhead

ABSTRACT

Showerheads for semiconductor processing equipment are disclosed that include various features designed to minimize or eliminate non-uniform gas delivery across the surface of a wafer due to gas flow transients within the showerhead.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/163,594, filed on May 24, 2016, and titled ANTI-TRANSIENTSHOWERHEAD,” which itself claims benefit of priority under 35 U.S.C. §119(e) to U.S. Provisional Application No. 62/166,612, filed on May 26,2015, and titled “ANTI-TRANSIENT SHOWERHEAD,” which are both herebyincorporated by reference herein in their entireties.

BACKGROUND

Semiconductor processing tools often include components designed todistribute process gases in a relatively even manner across asemiconductor substrate or wafer. Such components are commonly referredto in the industry as “showerheads.” Showerheads typically include afaceplate that fronts a semiconductor processing volume in whichsemiconductor substrates or wafers may be processed. The faceplate mayinclude a plurality of gas distribution ports that allow gas in theplenum volume to flow through the faceplate and into a reaction spacebetween the substrate and the faceplate (or between a wafer supportsupporting the wafer and the faceplate). In some instances, a showerheadmay be configured to distribute two different gases across asemiconductor substrate or wafer in a simultaneous fashion whileisolating the gases from each other within the showerhead. The gasdistribution ports are typically arranged such that the gas distributionacross the wafer results in substantially uniform substrate processing.

SUMMARY

One aspect of the disclosure pertains to an apparatus having: a firstgas inlet, a first surface, a plurality of first gas distribution ports,a second surface, a third surface interposed between the first surfaceand the second surface, a fourth surface interposed between the thirdsurface and the second surface, and a plurality of first gas flowpassages interposed between the first surface and the third surface. Insuch an apparatus, the first gas inlet may be configured to deliver afirst process gas through the first surface and the first gasdistribution ports may be configured to deliver the first process gasthrough the second surface.

The apparatus may have a first inlet plenum volume that is fluidicallyconnected with the first gas inlet, the first inlet plenum volume beingat least partially defined by the first surface and the third surface.The apparatus may further have a first gas distribution plenum volumethat is fluidically connected with the first gas distribution ports, thefirst gas distribution plenum volume being at least partially defined bythe second surface and the fourth surface.

The first gas flow passages may each have a first end that fluidicallyconnects that first gas flow passage with the first inlet plenum volumeand a second end that fluidically connects that first gas flow passagewith the first gas distribution plenum volume. Each first gas flowpassage may be substantially the same overall length, extend away fromthe first inlet plenum volume at the first end, and include between 140°and 200° of bends between the first end and the second end such that thesecond end of that first gas flow passage is oriented towards the firstinlet plenum volume.

In some embodiments, the second end of each first gas flow passage maybe fluidically connected with the first gas distribution plenum volumeby a corresponding first hole passing through the fourth surface; eachfirst hole may have a nominal hole diameter. In some embodiments, aplurality of first raised bosses may extend up from the second surfacetowards the fourth surface, each first raised boss centered on one ofthe first holes and having a nominal boss diameter. In some suchembodiments, each first raised boss may be offset from the fourthsurface by a distance of between 0.025 mm and 1.2 mm. In other oradditional such embodiments, each first raised boss may be offset fromthe fourth surface by a distance of between 1/11th and 1/13th of thenominal diameter. In yet other additional or alternative suchembodiments, each first raised boss may be offset from the fourthsurface by a distance that is less than twice the difference between thenominal boss diameter and the nominal hole diameter and is greater than0.2 times the difference between the nominal boss diameter and thenominal hole diameter.

In some embodiments, a different subset of first gas distribution portsmay be adjacent to each of the first raised bosses and each first raisedboss may be centered between the first gas distribution ports in theplurality of first gas distribution ports adjacent to that first raisedboss.

In some embodiments, a plurality of first support columns may spanbetween the second surface and the fourth surface.

In certain embodiments, the first holes may have diameters between 1.5mm and 3 mm, and in certain alternative or additional embodiments, thefirst bosses may have diameters that are between 5 mm and 8 mm.

In some embodiments, the apparatus may also include a plurality of firstpeninsulas. Each first peninsula may protrude into the first inletplenum volume, and the second end of one or more of the first gas flowpassages may extend into each of the first peninsulas. In such anembodiment, the second end of the first gas flow passages in the firstpeninsulas may be closer to the first center point of the first inletplenum volume than the first ends of such first gas flow passages.

In some embodiments, the first gas flow passages may include between150° and 190° of bends between the first end and the second end. In someembodiments, each of the first gas flow passages may have a lengthwithin ±30%, ±20, ±10%, or ±5% of the other first gas flow passages.

In some embodiments, each of the first gas flow passages may have aconstant cross-sectional area along its length. In some embodiments, thefirst end of each of the first gas flow passages may be equidistant froma first axis of the apparatus. In some embodiments, the apparatus mayinclude between 20 and 100 first gas flow passages.

In some embodiments, the apparatus may also include: a second gas inlet,a fifth surface, a plurality of second gas distribution ports, a sixthsurface, a seventh surface interposed between the fifth surface and thesixth surface, an eighth surface interposed between the sixth surfaceand the seventh surface, and a plurality of second gas flow passagesinterposed between the fifth surface and the seventh surface. In suchembodiments, the second gas inlet may be configured to deliver a secondprocess gas through the fifth surface and the second gas distributionports may be configured to deliver the second process gas through thesixth surface.

In some embodiments, the apparatus may have a second inlet plenum volumethat is fluidically connected with the second gas inlet. The secondinlet plum volume may be at least partially defined by the fifth surfaceand the seventh surface. The apparatus may further have a second gasdistribution plenum volume that is fluidically connected with the secondgas distribution ports and the second gas distribution plenum volume maybe at least partially defined by the sixth surface and the eighthsurface.

In some embodiments, the second gas flow passages may each have a firstend that fluidically connects that second gas flow passage with thesecond inlet plenum volume and a second end that fluidically connectsthat second gas flow passage with the second gas distribution plenumvolume. Each second gas flow passage may be substantially the sameoverall length, extend away from the second inlet plenum volume at thefirst end, and include between 140° and 200° of bends between the firstend and the second end such that the second end of that second gas flowpassage is oriented towards the first inlet plenum volume.

In some embodiments, the second end of each first gas flow passage ofsuch an apparatus may be fluidically connected with the first gasdistribution plenum volume by a corresponding first hole passing throughthe fourth surface; each first hole may have a nominal hole diameter. Insome cases, a plurality of first raised bosses may extend up from thesecond surface towards the fourth surface, and each first raised bossmay be centered on one of the first holes and may have a nominal bossdiameter. In such an embodiment, the second end of each second gas flowpassage may also be fluidically connected with the second gasdistribution plenum volume by a corresponding second hole passingthrough the eighth surface; each second hole may have a nominal holediameter. In some cases, a plurality of second raised bosses extend upfrom the sixth surface towards the eighth surface, where each secondraised boss is centered on one of the second holes and may have anominal boss diameter.

In some cases, each first raised boss may be offset from the fourthsurface and/or each second raised boss may be offset from the eighthsurface by a distance of between 0.025 mm and 1.2 mm. In other oradditional cases, each first raised boss may be offset from the fourthsurface and/or each second raised boss may be offset from the eighthsurface by a distance of between 1/11th and 1/13th of the respectivenominal diameter of each raised boss. In yet other cases, each firstraised boss may be offset from the fourth surface and/or each secondraised boss may be offset from the eighth surface by a distance that isless than twice the difference between the nominal boss diameter and therespective nominal hole diameter and is greater than 0.2 times thedifference between the nominal boss diameter and the respective nominalhole diameter.

In certain embodiments, the apparatus may have one or more additionalfirst gas inlets, and the first inlet plenum volume may be partitionedinto multiple first inlet plenum sub-volumes which are each fed by adifferent one of the first gas inlets.

In certain embodiments, the first inlet plenum volume and the first gasdistribution plenum volume may be interposed between the second inletplenum volume and the second gas distribution plenum volume. In otherembodiments, the first inlet plenum volume and the second gasdistribution plenum volume may be interposed between the second inletplenum volume and the first gas distribution plenum volume.

In some embodiments, a different subset of first gas distribution portsin the apparatus are adjacent to each of the first raised bosses andeach first raised boss is centered between the first gas distributionports adjacent to that first raised boss.

In some embodiments, a different subset of second gas distribution portsin the modified apparatus are adjacent to each of the second raisedbosses and each second raised boss is centered between the second gasdistribution ports adjacent to that second raised boss.

In certain embodiments, the apparatus may also contain a plurality offirst support columns that span between the second surface and thefourth surface and a plurality of second support columns that spanbetween the sixth surface and the eighth surface.

In some embodiments, the apparatus may also include a plurality of firstpeninsulas, each first peninsula protruding into the first inlet plenumvolume and the second end of one or more of the first gas flow passagesextending into each of the first peninsulas. In such an embodiment, thesecond end of the first gas flow passages in the first peninsulas may becloser to the first center point of the first inlet plenum volume thanthe first ends of those first gas flow passages.

In some embodiments, the apparatus may also have a plurality of secondpeninsulas, each second peninsula protruding into the second inletplenum volume and the second end of one or more of the second gas flowpassages extending into each of the second peninsulas. In such anembodiment, the second end of the second gas flow passages in the secondpeninsulas may be closer to the second center point of the second inletplenum volume than the first ends of those second gas flow passages.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an isometric exploded view of an example anti-transientshowerhead.

FIG. 2 depicts a plan view of a first partition plate of the exampleanti-transient showerhead of FIG. 1.

FIG. 3 depicts a plan view of a faceplate of the example anti-transientshowerhead of FIG. 1.

FIG. 4 depicts an isometric cutaway view of the example anti-transientshowerhead of FIG. 1.

FIG. 5 depicts a section view of the example anti-transient showerheadof FIG. 1.

FIG. 6 depicts a detail view of a portion of FIG. 5.

FIG. 7 depicts an isometric exploded view of an example anti-transient,dual-plenum showerhead.

FIG. 8 depicts a plan view of a first partition plate of the exampleanti-transient, dual-plenum showerhead of FIG. 7.

FIG. 9 depicts a plan view of a baffle plate of the exampleanti-transient, dual-plenum showerhead of FIG. 7.

FIG. 10 depicts a plan view of a second partition plate of the exampleanti-transient, dual-plenum showerhead of FIG. 7.

FIG. 11 depicts a plan view of a faceplate of the exampleanti-transient, dual-plenum showerhead of FIG. 7.

FIG. 12 depicts an isometric cutaway view of the example anti-transient,dual-plenum showerhead of FIG. 7.

FIGS. 1 through 12 are drawn to scale within each Figure, although thescale from Figure to Figure may vary.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the presented concepts. Thepresented concepts may be practiced without some or all of thesespecific details. In other instances, well known process operations havenot been described in detail so as to not unnecessarily obscure thedescribed concepts. While some concepts will be described in conjunctionwith the specific embodiments, it will be understood that theseembodiments are not intended to be limiting.

In this application, the terms “semiconductor wafer,” “wafer,”“substrate,” “wafer substrate,” and the like are used interchangeably. Awafer or substrate used in the semiconductor device industry typicallyhas a diameter of 200 mm, 300 mm, or 450 mm, but may also benon-circular and of other dimensions. In addition to semiconductorwafers, other work pieces that may take advantage of this inventioninclude various articles such as printed circuit boards, magneticrecording media, magnetic recording sensors, mirrors, optical elements,micro-mechanical devices and the like.

Several conventions may have been adopted in some of the drawings anddiscussions in this disclosure. For example, reference is made atvarious points to “volumes,” e.g., “plenum volumes.” These volumes maybe generally indicated in various Figures, but it is understood that theFigures and the accompanying numerical identifiers represent anapproximation of such volumes, and that the actual volumes may extend,for example, to various solid surfaces that bound the volumes. Varioussmaller volumes, e.g., gas inlets or other holes leading up to aboundary surface of a plenum volume, may be fluidly connected to thoseplenum volumes.

It is to be understood that the use of relative terms such as “above,”“on top,” “below,” “underneath,” etc. are to be understood to refer tospatial relationships of components with respect to the orientations ofthose components during normal use of a showerhead or with respect tothe orientation of the drawings on the page. In normal use, showerheadsare typically oriented so as to distribute gases downwards towards asubstrate during substrate processing operations.

Semiconductor fabrication often requires that process gases, such asdeposition and etch gases, be flowed in a uniform or controlled mannerover a semiconductor wafer or substrate undergoing processing. To thatend, a “showerhead,” also referred to herein as a gas distributionmanifold and sometimes also referred to as a gas distributor, may beused to distribute gases across the surface of a wafer. When gas isinitially flowed into a showerhead, it may take varying amounts of timefor the initial gas flow to reach each of the gas distribution portsarranged across the faceplate of the showerhead, which may result in anon-uniform gas distribution across the face of the showerhead. Afterthe gas flow through the showerhead has stabilized, e.g., after thepressure environment within the plenum volume(s) of the showerhead hasstabilized, the gas flow may be much more uniform. During the initialtransient period, however, the pressure within the plenum volumes mayfluctuate, and this may result in unbalanced flow characteristics acrossthe faceplate. Due to the unpredictability of such transient flow, thetransient flow period is typically “lost” time during a semiconductorprocess.

During long-duration semiconductor processes, e.g., processes havingcycle times of hundreds of seconds or longer, the transient period,which may be a few seconds, may constitute a relatively small portion ofthe overall cycle duration, and thus the “lost” time may constitute arelatively small fraction of the overall cycle time. In short durationsemiconductor processes, however, such as atomic layer deposition (ALD),the transient period may have a much more pronounced effect. Forexample, in ALD, gas delivery times on the order of seconds or tenths ofa second are common—if each cycle must also accommodate the time lostdue to transients, then it is easy to see how transient loss maydramatically lengthen the overall process time.

The anti-transient showerheads discussed herein provide a new mechanismfor minimizing or reducing transient gas flow response, or eveneliminating it entirely for the relevant cycle time, from semiconductorprocessing systems.

Anti-transient showerheads, generally speaking, may be configured withat least two plenums—a gas inlet plenum and a gas distribution plenum.Each of these plenums may define a separate plenum volume. Suchshowerheads may also include a multitude of gas flow passages that arefluidically connected with the gas inlet plenum volume at a first endand with the gas distribution plenum volume at the second end. In manycases, a partition plate may separate the gas inlet plenum from the gasdistribution plenum, and the gas flow passages may be machined into oneface of the partition plate; holes located at the second end of the gasflow passages may allow gas that flows from the inlet plenum volume andinto the gas flow passages to then pass through the partition plate andinto the gas distribution plenum volume. The purpose of the gas flowpassages is to deliver substantially equal proportions of gas from theinlet plenum volume to distributed locations with the gas distributionplenum volume. For example, the second ends of the gas flow passages maybe arranged in a plurality of concentric or near-concentric, e.g.,having center points within a few millimeters of each other, circularpatterns so as to deliver gas into the gas distribution plenum volume atvarious distributed locations. Thus, some second ends may be locatednear the periphery of the gas distribution plenum volume, some towardsthe center of the gas distribution plenum volume, and some in betweenthose two locations.

Each gas flow passage may have substantially the same length, e.g.,having ±5% variation in length, and may maintain a similarcross-sectional profile or area along its length, e.g., each gas flowpassage may have a constant cross-sectional area along its length. Eachgas flow passage may also include one or more bends that cause the gasflow passage to ultimately change direction by ±X degrees from somecommon angle, e.g., 170°±15° or ±20° between the first end and thesecond end. These bends may include, by way of example, a single bend of170°, two bends of 100° and 70°, three bends of 50°, 40°, and 80°, etc.The number of bends in each gas flow passage may be the same, or mayvary from passage to passage—regardless of how many bends are in eachpassage, however, the total bend angle for each passage may be withinthe limits stated above. It is to be understood that the “total bendangle” is the total of the absolute values of the bend angles for agiven gas flow passage. Thus, if a gas flow passage undergoes a bend of90° to the left and then 90° to the right, the total bend angle would be180°, not 0°. By including the same nominal total bend angle,cross-sectional area profile, and passage length in each gas flowpassage, the gas flow passages may be caused to exhibit substantiallysimilar flow resistance, which may cause gas that is flowed through thegas flow passages to flow at the same rates through all of the passages,even during transient flow. In some implementations, the total bendangle may be between, but not limited to, 140° to 200° degrees, i.e.,more relaxed or more bent than the 170°±15° discussed above.

Further performance increases may be obtained by including a pluralityof raised bosses that protrude up from the faceplate towards the holesthat deliver the gas from the gas flow passages to the gas distributionplenum volume. Each of these raised bosses may be centered underneath acorresponding one of the holes such that gas that exits the holeimpinges on the center of the raised boss, causing the gas to undergo achange of flow direction of approximately 90°, e.g., the gas flowchanges from flowing along the hole axis to flowing in a directiongenerally parallel to the faceplate. The raised boss thus acts as a“mini-baffle” that serves to further distribute the gas in a more evenmanner throughout the gas distribution plenum volume.

FIG. 1 depicts an isometric exploded view of an example anti-transientshowerhead. As can be seen, an anti-transient showerhead 100 is shown.The showerhead 100 includes a stem 180 that may be used to deliver afirst process gas to the showerhead 100; the stem may provide gas to afirst gas inlet 112 (alternatively, the stem 180 also may be thought ofas the first gas inlet 112). The stem 180 may connect with a backplate102, e.g., through a brazed, diffusion bonded, welded, or boltedconnection. The backplate 102 may, in turn, be mated with a firstpartition plate 108. The first partition plate 108 may include variousfeatures that are machined or otherwise formed into it that define afirst inlet plenum volume 142 and a plurality of first gas flow passages138. The first gas flow passages 138 may have first ends that arefluidically connected with the first inlet plenum volume 142 and thatare arranged along an outer perimeter of the first inlet plenum volume142; the first gas flow passages 138 may generally radiate outwards fromthis outer perimeter of the first inlet plenum volume 142 beforesubstantially reversing their direction by virtue of the above-mentionedbends in each first gas flow passage 138.

The showerhead 100 may also include a faceplate 104 that includes aplurality of first gas distribution ports 134 arranged in a patternacross the faceplate 104. The faceplate 104 may be mated to the firstpartition plate 108 such that a first gas distribution plenum volume 146is formed. The first gas distribution plenum volume 146 may befluidically connected with the first inlet plenum volume 142 by theplurality of first gas flow passages 138.

Generally speaking, the first inlet plenum volume 142 and the first gasdistribution plenum volume 146 may be bounded, at least in part, variousmajor surfaces. For example, the backplate 102 may provide a firstsurface 116 through which process gas may be introduced from the firstgas inlet 112 and into the first inlet plenum volume 142; the firstsurface 116 may thus act as one boundary for the first inlet plenumvolume 142. Similarly, the faceplate 104 may provide a second surface118 through which the process gas may be flowed from the first gasdistribution plenum volume 146 by way of the first gas distributionports 134; the second surface 118 may thus act as one boundary for thefirst gas distribution plenum volume 146. Similarly, the first partitionplate 108 may have a third surface 120 and a fourth surface 122, whichmay serve as further boundaries for the first inlet plenum volume 142and the first gas distribution plenum volume 146, respectively.

It is to be understood that these surfaces need not necessarily beprovided by the exact components depicted. In fact, in someimplementations, there may not even be discrete faceplates, backplates,or partition plates. For example, the showerhead 100 may be manufacturedas a monolithic structure, e.g., by using additive manufacturingtechniques such as direct laser metal sintering or, if a ceramicshowerhead is desired, a ceramic sintering process. In implementationswhere multiple plate structures are used, such as in the depictedexample, it may be desirable to include an indexing pin 106 or othersimilar feature to ensure that the various plates are lined upcorrectly. It is to be understood that if a multiple-plate structure isused, the various plates that form the overall showerhead structure maybe brazed or diffusion bonded together along their mating surfaces toprevent gas flow between the contacting surfaces of the plates.

Also visible in FIG. 1 are a plurality of first raised bosses 160, eachof which is positioned beneath the second end of the one of the firstgas flow passages 138. In addition to the first raised bosses, a numberof first support columns 164 may be optionally included. Unlike thefirst raised bosses 160, which do not contact the fourth surface 122,the first support columns 164 may provide structural support and athermally conductive path to the faceplate 104, and thus may extend toand contact the fourth surface 122 (and may be brazed or diffusionbonded to it for structural support).

From a practical perspective, it may be desirable to include a largenumber of gas flow passages in an anti-transient showerhead. However, asthe number of gas flow passages included in an anti-transient showerheadincreases, the size of the corresponding inlet plenum volume must alsoincrease to accommodate the increased number of junctions between eachgas flow passage and the inlet plenum volume along the perimeter of theinlet plenum volume. At some point, as the number of gas flow passagesis increased, the size of the inlet plenum volume may expand to a largeenough extent that it may be desirable to place some of the holes thatfeed gas from the gas flow passages to the gas distribution plenumvolume within the perimeter of the gas inlet plenum volume. In order todo so while maintaining fluidic isolation between each gas flow passage,a number of peninsulas may be included. Each peninsula may protrude intothe inlet plenum volume from the nominal outermost perimeter of theinlet plenum volume. Each peninsula may include one or more gas flowpassages that may be used to deliver gas to such locations.

FIG. 2 depicts a plan view of the first partition plate 108 of theexample anti-transient showerhead of FIG. 1. As can be seen in moredetail in this Figure, each first gas flow passage 138 has a bend 154that occurs at some point along the passage's length. Moreover, eachfirst gas flow passage 138 has substantially the same length as theother first gas flow passages 138, in this case, ^(˜)170 mm±5%. Forpurposes of illustration, the first gas flow passages 138 in thisexample are approximately 2 mm wide. Each first gas flow passage 138 isfluidically connected with the first inlet plenum volume 142 at a firstend 150 and is fluidically connected to the first gas distributionplenum volume 146 at a second end 152 by way of a first hole 156. As canbe seen, six of the first holes 156 are located within the outermostcircumference of the first inlet plenum volume 142; the first gas flowpassages 138 that provide gas to these first holes 156 are partitionedoff from the first inlet plenum volume 142 by peninsulas 168, whichextend into the first inlet plenum volume 142. As can be seen in theshowerhead 100, there are sixty first gas flow passages 138 radiatingout from the first inlet plenum volume 142. Such a high number of firstgas flow passages 138 would not be able to fit (at the indicated passagewidth) along the outer perimeter of the first inlet plenum volume 142 ifthe first inlet plenum volume was sized so as to be within the innermostpattern of first holes 156 (the first holes 156 that are located withinthe peninsulas 168).

FIG. 3 depicts a plan view of the faceplate 104 of the exampleanti-transient showerhead of FIG. 1. As can be seen, the first raisedbosses 160 are arranged in a relatively distributed manner throughoutthe first gas distribution plenum volume 146

FIG. 4 depicts an isometric cutaway view of the example anti-transientshowerhead of FIG. 1. As can be seen, each first hole 156 is positioneddirectly above a corresponding first raised boss 160. Gas that flowsinto the first inlet plenum volume 142 through the first gas inlet 112may generally reach the first ends 150 of all of the first gas flowpassages 138 at the same time and may, by virtue of the first gas flowpassages 138 being nominally the same length and having nominally thesame total bend angle and cross-sections along their length, reach thesecond ends 152 of the first gas flow passages 138 at generally the sametime. This has the result of introducing the gas into the first gasdistribution plenum volume at a plurality of points, e.g., each firsthole 156, more or less simultaneously. The first raised bosses 160 maythe act to further distribute the gas throughout the first gasdistribution plenum volume 146 such that the gas flows through the firstgas distribution ports 134 in a generally uniform manner, even when thegas flow within the showerhead 100 has not yet reached steady state.

FIG. 5 depicts a section view of the example anti-transient showerheadof FIG. 1. The various plates, e.g., the faceplate 104, the backplate102, and the first partition plate 108, are depicted, as well as thefirst surface 116, the second surface 118, the third surface 120, andthe fourth surface 122. FIG. 5 also indicates a circled area that isshow in more detail in FIG. 6.

FIG. 6 depicts a detail view of a portion of FIG. 5. This detail viewshows the second end 152 of one of the first gas flow passages 138, aswell as the first hole 156 that fluidically connects the first gas flowpassage 138 to the first gas distribution plenum volume 146. Alsodepicted in FIG. 6 is a first support column 164, which spans betweenthe second surface 118 and the fourth surface 122. Two first raisedbosses 160 are also visible, including one that is directly beneath thefirst hole 156. As is evident, the first raised boss 160 below the firsthole 156 is centered underneath the first hole 156. Moreover, a firstgap 176 exists between the first raised boss 160 and the fourth surface122. In the depicted example, the first hole 156 has a diameter of 2 mm,the first raised boss 160 a diameter of 6.5 mm, and the first gap 176 is0.5 mm. In several implementations, the first gap 176 may be a functionof the nominal diameter of the first raised boss 160 and may, in somesuch implementations, range from 1/11th of the raised boss nominaldiameter to 1/13th of the raised boss nominal diameter, e.g.,approximately 1/12th of the raised boss diameter. In otherimplementations, the first gap 176 may be a function of the nominaldiameter of the first raised boss 160 and the diameter of the first hole156, e.g., the first gap 176 may be selected such that the first gap 176divided by twice the difference between the first raised boss 160diameter and the first hole 156 diameter is between 0.1 and 1.

The previous example was directed at a showerhead 100 that only supportsflow of a single process gas. As discussed, the concepts discussedherein may be applied to multi-flow or multi-plenum showerheads as well.This concept is discussed in more detail below with respect to ashowerhead configured to flow two process gases simultaneously. Many ofthe structures in this dual-flow example correspond with structuresdiscussed previously with respect to the single-flow showerhead 100. Toavoid prolixity, these components may not be described again below; insuch cases, the previous discussion of similar structures in theshowerhead 100 may be referred to for a description. Components that aresimilar between the showerhead 100 and the dual-flow showerheaddiscussed below may share the last two digits of their drawing referencenumbers in common.

FIG. 7 depicts an isometric exploded view of an example anti-transient,dual-plenum showerhead. As can be seen, a stem 780 is provided thatallows for two separate gases to be supplied to a showerhead 700; thestem may be connected to a backplate 702. The stem 780 may include twosets of passages, one that includes a passage that runs along the centerof the stem 780, and the other that includes a circular array ofpassages that is interposed between that center passage and an outersleeve (the lower portion of the stem 780 shown). In this example, thecircular array of gas flow passages in the stem provides gas for a firstgas inlet 712 (six holes arrayed about the center hole of the backplate702), and the center gas flow passage provides gas for the second gasinlet 714 (the center hole in the backplate 702). The showerhead 700 mayalso include a first partition plate 708, a second partition plate 710,a baffle plate 778, and a faceplate 704.

FIG. 8 depicts a plan view of the first partition plate of the exampleanti-transient, dual-plenum showerhead of FIG. 7. The first partitionplate 708 is very similar to the first partition plate 108, but with atleast two differences. For example, there may be a raised center boss782 that is located at the center of the first inlet plenum volume 742;this raised center boss 782 may serve to decrease the size of the firstinlet plenum volume 742 to decrease the amount of time it takes to flowthe first process gas through the first inlet plenum volume, and mayalso, in some implementations, help even out the gas flow from the sixports that serve as the first gas inlet 712. In some implementations,the first inlet plenum volume may be partitioned into multiple firstinlet plenum sub-volumes, each fed by a different one of the first gasinlets. The other difference is that there are a number of second holes758 through the first partition plate 708.

FIG. 9 depicts a plan view of the baffle plate of the exampleanti-transient, dual-plenum showerhead of FIG. 7. In thisimplementation, the baffle plate 778 is very similar to the faceplate104, except that the first support columns 764 are more numerous and arearranged differently from the first support columns 164. As can be seenfrom FIG. 7, each first support column 764 corresponds in location toone of the second holes 758 in the first partition plate 708, and thecorresponding second hole 758 continues through the first support column764. Thus, the first support columns 764 not only provide structuralsupport and a thermally conductive pathway between the first partitionplate 708 and the baffle plate 778, but also provide an avenue for gasflow through the baffle plate that keeps such gas isolated from the gasthat is within the first gas distribution plenum volume 746. As with thefaceplate 104, the baffle plate 778 may include a plurality of firstraised bosses 760 that are each positioned beneath a first hole 756(shown later) that fluidically connects one of the first gas flowpassages 738 with the first gas distribution plenum volume 746. As withthe faceplate 104, the baffle plate 778 may include a plurality of firstgas distribution ports 734 that may supply gas from the first gasdistribution plenum volume 746 to either the second gas distributionplenum volume immediately beneath the first gas distribution plenum orto a wafer processing area beneath the showerhead 700.

FIG. 10 depicts a plan view of the second partition plate of the exampleanti-transient, dual-plenum showerhead of FIG. 7. The second partitionplate 710 may serve a function similar to the first partition plate 708,but with respect to the second gas inlet 714. As can be seen, aplurality of substantially equal-length second gas flow passages 740fluidly connects a second inlet plenum volume 744 with a second gasdistribution plenum volume 748 (see FIG. 11) via second holes 758; thesecond gas distribution plenum volume 748, in this example, is a plenumvolume formed between the baffle plate 778 and the faceplate 704. Thesecond gas flow passages 740, in this case, and as with the first gasflow passages 738, may have first ends 750 that connect with the secondinlet plenum volume 744 and second ends 752 that are fluidicallyconnected with the second holes 758. As can be seen, each second gasflow passage 740 may also include a bend 754 which may be similar to thebends 754 in the first gas flow passages 738, although, as can be seen,the bend angles may be more relaxed. Similar to the first peninsulas 768in the first inlet plenum volume 742, the second inlet plenum volume 744may also include a plurality of second peninsulas 770 that allow some ofthe second holes 758 to be located within the outer periphery of thesecond inlet plenum volume 744.

FIG. 11 depicts a plan view of the faceplate of the exampleanti-transient, dual-plenum showerhead of FIG. 7. The faceplate 704 mayinclude a plurality of second gas distribution ports 736 and a pluralityof first gas distribution ports 734. The second gas distribution plenumvolume 748 may be formed between the faceplate 704 and the baffle plate77, and may include a pattern of second raised bosses 762 that serve asmini-baffles for the second holes 758, much as the first raised bosses760 do for the first holes 756.

In some implementations, each first gas distribution port 734 in thebaffle plate 778 may be fluidically connected to the corresponding firstgas distribution port 734 in the faceplate 704 by a tubular structure784 that isolates the gas flowing through the first gas distributionports 734 from the gas flowing through the second gas distributionplenum volume 748 within the showerhead 700.

FIG. 12 depicts an isometric cutaway view of the example anti-transient,dual-plenum showerhead of FIG. 7, and may provide more insight into thestructure of the showerhead 700.

Similar to the first inlet plenum volume 742 and the first gasdistribution plenum volume 746, the second inlet plenum volume 744 andthe second gas distribution plenum volume 748 may also be bounded byvarious surfaces. These surfaces are indicated in FIG. 7. For example,the second inlet plenum volume 744 may be bounded, in part, by a fifthsurface 724 and a seventh surface 728, whereas the second gasdistribution plenum volume 748 may be bounded, in part, by a sixthsurface 726 and an eighth surface 730.

In multi-plenum showerheads, the positioning of the inlet plenums withrespect to the gas distribution plenums may be re-ordered as needed forany particular design—they need not be in the arrangement depicted. Forexample, in the depicted implementations, the first inlet plenum volumeand the first gas distribution plenum volume are bracketed between thesecond inlet plenum volume and the second gas distribution plenumvolume. In other implementations, however, this ordering may be altered.By way of non-limiting example, any of the following orders may also beused in various implementations of this concept:

Implementation Implementation Implementation Implementation 1 2 3 4First inlet Second inlet First inlet Second inlet plenum plenum plenumplenum volume volume volume volume Second inlet First inlet Second inletFirst inlet plenum plenum plenum plenum volume volume volume volumeSecond gas Second gas Second gas First gas distribution distributiondistribution distribution plenum volume plenum volume plenum volumeplenum volume First gas First gas First gas Second gas distributiondistribution distribution distribution plenum volume plenum volumeplenum volume plenum volumeIn such cases, plenum volumes for a first gas that have plenum volumesfor a second gas interposed between them may be fluidically connected bycausing the holes, e.g., the first holes, that fluidically connect theplenums for the first gas to pass between the gas flow passages for thesecond gas or through support columns within the plenum(s) for thesecond gas.

What is claimed is:
 1. An apparatus comprising: a first gas inlet; afirst surface, wherein the first gas inlet is configured to deliver afirst process gas through the first surface; a plurality of first gasdistribution ports; a second surface, wherein the plurality of first gasdistribution ports are configured to deliver the first process gasthrough the second surface; a third surface interposed between the firstsurface and the second surface; a fourth surface interposed between thethird surface and the second surface; a plurality of first raised bossesthat extend up from the second surface towards the fourth surface; aplurality of first gas flow passages interposed between the firstsurface and the third surface; and a plurality of first holes passingthrough the fourth surface, wherein: the first surface and the thirdsurface at least partially define a first inlet plenum volume that isfluidically connected with the first gas inlet, the second surface andthe fourth surface at least partially define a first gas distributionplenum volume that is fluidically connected with each first gasdistribution port of the plurality of first gas distribution ports, eachfirst gas flow passage of the plurality of first gas flow passages has acorresponding first end that fluidically connects with the first inletplenum volume and a corresponding second end that fluidically connectswith the first gas distribution plenum volume via a corresponding firsthole of the plurality of first holes, each first raised boss of theplurality of first raised bosses is centered on a corresponding firsthole of the plurality of first holes and has a corresponding top surfacefacing the fourth surface that is offset from the fourth surface by acorresponding first distance, and each first gas flow passage of theplurality of first gas flow passages has a flow resistance that issubstantially similar to the flow resistance of each other first gasflow passage.
 2. The apparatus of claim 1, wherein each of thecorresponding first distances is between 0.025 mm and 1.2 mm for thecorresponding first raised boss of the plurality of first raised bosses.3. The apparatus of claim 1, wherein: each first hole has a holediameter, and each of the corresponding first distances is less thantwice a difference between a nominal boss diameter for the correspondingfirst raised boss of the plurality of first raised bosses and thecorresponding hole diameter and is greater than 0.2 times the differencebetween the nominal boss diameter for the corresponding first raisedboss of the plurality of first raised bosses and the corresponding holediameter.
 4. The apparatus of claim 1, wherein the first raised bossesof the plurality of first raised bosses each have a nominal diameter ofbetween 5 mm and 8 mm.
 5. The apparatus of claim 1, wherein each firstraised boss of the plurality of first raised bosses has a nominaldiameter and a corresponding first distance of between 1/11^(th) and1/13^(th) of the corresponding nominal diameter.
 6. The apparatus ofclaim 1, wherein different subsets of the first gas distribution portsof the plurality of first gas distribution ports are adjacent to each ofthe first raised bosses of the plurality of first raised bosses and eachfirst raised boss of the plurality of first raised bosses is centeredbetween the first gas distribution ports of a corresponding subset ofthe different subsets of the first gas distribution ports of theplurality of first gas distribution ports.
 7. The apparatus of claim 1,further comprising a plurality of first support columns, wherein eachfirst support column of the plurality of first support columns spansbetween the second surface and the fourth surface.
 8. The apparatus ofclaim 1, wherein each first hole of the plurality of first holes has adiameter of between 1.5 mm and 3 mm and wherein each first raised bossof the plurality of first raised bosses has a diameter of between 5 mmand 8 mm.
 9. The apparatus of claim 1, further comprising a plurality offirst peninsulas, wherein: the first inlet plenum volume has a firstcenter point, each first peninsula of the plurality of first peninsulasprotrudes into the first inlet plenum volume, and the second end of oneor more of the first gas flow passages of the plurality of first gasflow passages extends into a corresponding first peninsula of theplurality of first peninsulas and is closer to the first center pointthan the corresponding first end of the corresponding first gas flowpassage of the plurality of first gas flow passages.
 10. The apparatusof claim 1, wherein each first gas flow passage is substantially thesame overall length, extends away from the first inlet plenum volume atthe first end, and includes between 140° and 200° of bends between thefirst end and the second end such that the second end of that first gasflow passage is oriented towards the first inlet plenum volume.
 11. Theapparatus of claim 1, wherein each first gas flow passage of theplurality of first gas flow passages includes between 150° and 190° ofbends between the corresponding first end and the corresponding secondend.
 12. The apparatus of claim 1, wherein the length of each first gasflow passage of the plurality of first gas flow passages is within ±5%of the lengths of the other first gas flow passages in the plurality offirst gas flow passages.
 13. The apparatus of claim 1, wherein thelength of each first gas flow passage of the plurality of first gas flowpassages is within ±10% of the lengths of the other first gas flowpassages in the plurality of first gas flow passages.
 14. The apparatusof claim 1, wherein the length of each first gas flow passage of theplurality of first gas flow passages is within ±20% of the lengths ofthe other first gas flow passages in the plurality of first gas flowpassages.
 15. The apparatus of claim 1, wherein each first gas flowpassage of the plurality of first gas flow passages has a length within±30% of the other first gas flow passages.
 16. The apparatus of claim 1,wherein the cross-sectional area of each first gas flow passage of theplurality of first gas flow passages along the length of thecorresponding first gas flow passage of the plurality of first gas flowpassages is constant.
 17. The apparatus of claim 1, wherein thecorresponding first end of each first gas flow passage of the pluralityof first gas flow passages is equidistant from a first axis of theapparatus.
 18. The apparatus of claim 1, wherein there are between 20and 100 first gas flow passages in the plurality of first gas flowpassages.
 19. The apparatus of claim 1, further comprising: a second gasinlet; a fifth surface, wherein the second gas inlet is configured todeliver a second process gas through the fifth surface; a plurality ofsecond gas distribution ports; a sixth surface, wherein the plurality ofsecond gas distribution ports are configured to deliver the secondprocess gas through the sixth surface; a seventh surface interposedbetween the fifth surface and the sixth surface; an eighth surfaceinterposed between the sixth surface and the seventh surface; aplurality of second gas flow passages interposed between the fifthsurface and the seventh surface; and a plurality of second holes passingthrough the eighth surface, wherein: the fifth surface and the seventhsurface at least partially define a second inlet plenum volume that isfluidically connected with the second gas inlet, the sixth surface andthe eighth surface at least partially define a second gas distributionplenum volume that is fluidically connected with each second gasdistribution port of the plurality of second gas distribution ports,each second gas flow passage of the plurality of second gas flowpassages has a corresponding first end that fluidically connects withthe second inlet plenum volume and a corresponding second end thatfluidically connects with the second gas distribution plenum volume viaa corresponding second hole of the plurality of second holes, and eachsecond gas flow passage of the plurality of second gas flow passages hasa flow resistance that is substantially similar to the flow resistanceof each other second gas flow passage.
 20. The apparatus of claim 19,wherein: a plurality of second raised bosses extends up from the sixthsurface towards the eighth surface, each second raised boss of theplurality of second raised bosses is centered on a corresponding secondhole of the plurality of second holes, and each second raised boss ofthe plurality of second raised bosses has a corresponding top surfacefacing the eighth surface that is offset from the eighth surface by asecond distance.
 21. The apparatus of claim 20, wherein the first gasinlet includes a plurality of ports and the first inlet plenum volume ispartitioned into multiple first inlet plenum sub-volumes, each firstinlet plenum sub-volume of the multiple first inlet plenum sub-volumesassociated with a different port of the plurality of ports.
 22. Theapparatus of claim 20, wherein the first inlet plenum volume, the secondinlet plenum volume, the first gas distribution plenum volume, and thesecond gas distribution plenum volume are arranged in a stackedconfiguration and in an order selected from the group consisting of: (i)second inlet plenum volume, first inlet plenum volume, first gasdistribution plenum volume, and second gas distribution plenum volume;(ii) second inlet plenum volume, first inlet plenum volume, second gasdistribution plenum volume, and first gas distribution plenum volume;(iii) second inlet plenum volume, second gas distribution plenum volume,first inlet plenum volume, and second gas distribution plenum volume;(iv) first inlet plenum volume, second inlet plenum volume, first gasdistribution plenum volume, and second gas distribution plenum volume;and (v) first inlet plenum volume, second inlet plenum volume, secondgas distribution plenum volume, and first gas distribution plenumvolume.
 23. The apparatus of claim 21, wherein different subsets of thefirst gas distribution ports of the plurality of first gas distributionports are adjacent to each of the first raised bosses of the pluralityof the first raised bosses and each first raised boss of the pluralityof first raised bosses is centered between the first gas distributionports of a corresponding subset of the different subsets of the firstgas distribution ports of the plurality of first gas distribution ports.24. The apparatus of claim 21, wherein different subsets of the secondgas distribution ports of the plurality of second gas distribution portsare adjacent to each of the second raised bosses of the plurality ofsecond raised bosses and each second raised boss of the plurality ofsecond raised bosses is centered between the second gas distributionports of a corresponding subset of the different subsets of the secondgas distribution ports of the plurality of second gas distributionports.
 25. The apparatus of claim 20, further comprising a plurality offirst support columns and a plurality of second support columns,wherein: each first support column of the plurality of first supportcolumns spans between the second surface and the fourth surface, andeach second support column of the plurality of second support columnsspans between the sixth surface and the eighth surface.
 26. Theapparatus of claim 20, further comprising a plurality of firstpeninsulas, wherein: the first inlet plenum volume has a first centerpoint, each first peninsula of the plurality of first peninsulasprotrudes into the first inlet plenum volume, and the second end of oneor more of the first gas flow passages of the plurality of first gasflow passages extends into a corresponding first peninsula of theplurality of first peninsulas and is closer to the first center pointthan the corresponding first end of the corresponding first gas flowpassage of the plurality of first gas flow passages.
 27. The apparatusof claim 20, further comprising a plurality of second peninsulas,wherein: the second inlet plenum volume has a second center point, eachsecond peninsula of the plurality of second peninsulas protrudes intothe second inlet plenum volume, the second end of one or more of thesecond gas flow passages of the plurality of second gas flow passagesextends into a corresponding second peninsula of the plurality of secondpeninsulas and is closer to the second center point than thecorresponding first end of the corresponding second gas flow passage ofthe plurality of second gas flow passages.